1. Field of the Invention
This invention relates to sulfurized esters of olefinic carboxylic acids and to lubricating oil compositions containing these sulfurized esters as extreme-pressure agents. Such compositions exhibit extreme-pressure lubricating properties and are useful in cutting oils and for lubricating relatively moving parts such as in power transmission assemblies, gear trains and engines, particularly internal combustion engines.
Metal-cutting oils should be light-colored for good visibility of the work piece. Pleasant, or at least mild, odors are required for the health and comfort of the machine operator. In addition, the cutting oils must provide extreme-pressure lubrication for the work tool in order to provide the longest possible tool life before resharpening or replacement. In other lubricating applications where the operator is not exposed to vapors from the oil and visibility of the lubricated part is not crucial, color and odor of the oil may not be as important as extreme-pressure lubrication and antioxidant protection. However, odor and appearance are important to those who must prepare the lubricating oil additives, compound the oils and handle the oils as they are being used.
The reaction products of sulfur and olefinic compounds such as cracked wax, lard oil and sperm whale oil are dark brown or black even when diluted to the final use levels with oil. In addition, these compounds are malodorous, smelling of hydrogen sulfide and mercaptan by-products. Previously, light-colored, mild-smelling sulfur compounds for use in cutting oils have been made by chlorination or sulfochlorination followed by treatment with sodium polysulfide. This multi-step indirect process is expensive and, accordingly, the cutting oils prepared therefrom are expensive.
What is needed are light-colored, mild-smelling lubricating oil compositions which can be prepared from inexpensive materials by an inexpensive, preferably one-step, process. This invention fulfills this need rather nicely.
2. Prior Art
Smith, U.S. Pat. No. 2,683,119, describes compositions for imparting oiliness and film strength to lubricating oils. The compositions have at least two esterified carboxylic acid groups and at least one sulfur atom in a thiolinkage. All of the illustrated examples of suitable acids contain allylic hydrogen atoms.
Hutchinson et al, U.S. Pat. No. 3,740,333, disclose compositions useful as substitutes for sperm oil. The compositions are blends of triglycerides and wax esters. The was esters are derived from unsaturated fatty acids containing 18, 20 or 22 carbon atoms. The triglycerides are of the same fatty acids. The blend of the wax ester and triglycerides is sulfurized by conventional means.